Rare Earths In Application And Research Of 7075 Aluminum Alloy

In this paper,7075aluminum alloy and rare earth (La) are studied as the object,which aluminum alloy and rare earth resources are major characteristics of my country. The qualified ingot are hot rolled and cold rolled,and then the sheets are soluted and two-aging treated. In order to determine rare earth optimal amount,The Universal Tensile Machine is used for the mechanical test,which can study tensile strength and elongation of RE-7075aluminum alloy.The microstructure of RE-7075aluminum alloy and the mechanism of RE in the microstructure are analyzed by some modern analytical instruments which including OM(optical microscope) EDS(energy dispersive spectrometer), SEM(scanning electron microscope) and XRD(X-ray diffraction) which observe the microstructure, grain size and distribution, the shape of strengthen phase, size changes and the phase composition.The results show that1. The rare earth elements can significantly improve the as cast microstructure on7075Al alloy. The refinement effects are very good when its content is0.2%to0.5%,refined the best when RE elments achieve to0.3%. The grains become larger again, refinement results become worse when RE content is0.5%.Which is main power source of refinement. Its can produce phase of (LaAlCuMgZn)、(LaAlCu),which play the role on undercooling increased, resulting in the second phase with rare earth of metamorphism and its atomic radius of a large, strong activity of these reasons in the alloy.Besides, rare earth elements can be drawn with greater cohesion, have played a role in a number of micro-alloying.2. The primary phase of matrix microstructure contain α(Al)、T(Al2Mg3Zn3) and grain boundary microstructure include α(Al)、Al2Cu、AlCuMg4La4after homogenizing annealing. The alloy’s microstructure was uniform,reduced the volume fraction of second phase,increased supersaturation of matrix and eliminated gradually dendritic segregation and the conductivity and the hardness reduced in homogenizing annealing state.3. The microstructure takes place the phenomenon of over-burning when rolling temperature beyond480℃. These sheets manifest mainly brittle fracture under the tensile stress. The primary phase of microstructure contain a(Al)、AlLa4、Al2Zn3、AlMgZnCuLa、LaMgZn、 AlMg4Zn11There are needle-like or rod-like grains in the elongation-direction and the fibrous or streamlined grains in the rolled-direction of hot rolled sheet’s microstructure.Along with cold working advance, the softening annealing, the organizational structure nonuniform and so on have initiated the static reply and the static recrystallization. However, these mechanisms which cause the ramollescence occupied the dominant position.4. The RE can inhibit the recrystallization of the matrix at high temperature. The the large second-phase volume fraction is reduced,the matrix solution saturation is increased and the dendritic segregation was eliminated under appropriate solution. The primary phase of microstructure contain a(Al)、MgZn2、Al2Cu、Cu2MgLa after solution.The synthetical mechanical properties of hot rolled sheet of0.3%RE-7075Al alloy exceeds cold rolled sheet after the two-step aging treatment.Compare to unadding RE,it is a certain improve that the tensile strength, elongation and Brinell hardness.